Platform balance

ABSTRACT

The present disclosure is directed to a platform balance that is suitable for transmitting forces and moments in a plurality of directions. The platform balance is adapted to support a test specimen, such as a large vehicle, in a test environment such as a wind tunnel. The platform balance includes a frame support and at least three spaced-apart transducers coupled to the frame support. Each of the transducers is sensitive about two orthogonal sensed axes. The transducers cooperate to provide signals indicative of forces and moments with respect to at least two orthogonal axes. Each transducer includes a transducer body having a support coupled to a sensor body along an axis of compliance. The sensor body is adapted to deflect about the two orthogonal sensed axes where the sensed axes are mutually orthogonal to the axis of compliance.

REFERENCE TO CO-PENDING APPLICATION

This patent application is a divisional and claims priority toco-pending continuation-in-part United States patent applicationentitled “Platform Balance”, filed on Aug. 8, 2006, assigned Ser. No.11/501,6650 (now U.S. Pat. No. 7,788,984), which claims the benefit ofSer. No. 11/369,211, filed on Mar. 6, 2006, which claims the benefit ofUnited States provisional patent application entitled “PlatformBalance,” filed Mar. 7, 2005 and assigned Ser. No. 60/659,162, and whereapplication Ser. No. 11/369,211 also is a continuation-in-part andclaims priority to co-pending United States patent application entitled“Platform Balance”, filed on Dec. 3, 2004 and assigned Ser. No.11/003,943, and where application Ser. No. 11/003,943 claims the benefitof United States provisional patent application entitled “PlatformBalance”, filed on Dec. 4, 2003, and assigned Ser. No. 60/526,954. Eachof the foregoing applications is incorporated herein by reference intheir entirety.

BACKGROUND

The discussion below is merely provided for general backgroundinformation and is not intended to be used as an aid in determining thescope of the claimed subject matter.

The present disclosure relates to devices that transmit and measurelinear forces along and moments about three orthogonal axes. Moreparticularly, the present disclosure relates to devices that areparticularly well suited to measure forces and moments upon a testspecimen in a test environment, such as in a wind tunnel.

The measurement of loads, both forces and moments, with accuracy andprecision is important to many applications. A common use, where severalmoments and forces need to be measured, is in the testing of specimensin a wind tunnel. Test specimens can be placed on a platform balancelocated in a pit of the wind tunnel. The platform balance can be adaptedto receive a vehicle or other large test specimen, rather than merely ascale model of the vehicle. Actual vehicles, rather than scale models ofthe vehicles, allows the designer to determine actual measurements ofprototypes, rather than merely inferential measurements. If the testspecimen is a vehicle with wheels, the platform balance can be equippedwith a rolling belt to rotate the wheels, which can make a significantimprovement in measurement accuracy.

Six components of force and moment act on a test specimen on theplatform balance in the wind tunnel. These six components are known aslift force, drag force, side force, pitching moment, yawing moment, androlling moment. The moments and forces that act on the test specimen areusually resolved into three components of force and three components ofmoment with transducers that are sensitive to the components. Each ofthe transducers carries sensors, such as strain gages, that areconnected in combinations that form Wheatstone bridge circuits. Byappropriately connecting the sensors, resulting Wheatstone bridgecircuit unbalances can be resolved into readings of the three componentsof force and three components of moment.

Platform balances have a tendency to be susceptible to various physicalproperties of the test environment that can lead to inaccuratemeasurements without additional compensation. For example, temperaturetransients in the wind tunnel can result in thermal expansion of theplatform balance that can adversely affect the transducers. In addition,large test specimens are prone to create large thrust loads on thetransducers that can cause inaccurate measurements. Accordingly, thereis a continuing need to develop a platform balance suitable for use withlarge test specimens.

SUMMARY

This Summary and Abstract are provided to introduce some concepts in asimplified form that are further described below in the DetailedDescription. This Summary and Abstract are not intended to identify keyfeatures or essential features of the claimed subject matter, nor arethey intended to be used as an aid in determining the scope of theclaimed subject matter. In addition, the description herein provided andthe claimed subject matter should not be interpreted as being directedto addressing any of the short-comings discussed in the Background.

The present disclosure is directed to a platform balance that issuitable for transmitting forces and moments in a plurality ofdirections. The platform balance is adapted to support a test specimen,such as a large vehicle, in a test environment such as a wind tunnel.The platform balance includes a frame support and at least threespaced-apart transducers coupled to the frame support. Each of thetransducers is sensitive about two orthogonal sensed axes. Thetransducers cooperate to provide signals indicative of forces andmoments with respect to at least two orthogonal axes. In one example,the frame support includes a first perimeter frame and a secondperimeter frame. The platform balance of this example includes fourspaced-apart transducers coupling the first perimeter frame to thesecond perimeter frame. Transducers sensitive about two orthogonalsensed axes do not suffer from the effects of thermal expansion of theframe support and reject the large thrust loads present in transducerssensitive about three orthogonal sensed axes.

The present disclosure is also directed to a transducer body having asupport coupled to a sensor body along an axis of compliance. The sensorbody is adapted to deflect about the two orthogonal sensed axes wherethe sensed axes are mutually orthogonal to the axis of compliance. Inone aspect, the support includes a pair of clevis halves disposed onopposite sides of the sensor body along the axis of compliance.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plan view of a platform balance constructed in accordancewith the present disclosure.

FIG. 2 is an elevation view of the platform balance of FIG. 1 havingadditional features and is suitable for receiving a test specimen.

FIG. 3 is an elevation view of the platform balance of FIG. 2, andhaving an exemplary test specimen.

FIG. 4 is a top view of a transducer constructed in accordance with thepresent disclosure and included in the platform balance of FIG. 1.

FIG. 5 is a front view of the transducer of FIG. 4.

FIG. 6 is a side view of the transducer of FIG. 4.

FIG. 7 is a detailed view of a portion of the transducer of FIG. 4.

FIG. 8 is a side view of another transducer constructed in accordancewith the present disclosure.

FIG. 9 is a front view of another transducer constructed in accordancewith the present disclosure.

FIG. 10 is a side view of the transducer of FIG. 9.

FIG. 11 is a side view of yet another transducer constructed inaccordance with the present disclosure.

FIG. 12 is an exemplary torque sensing circuit.

FIG. 13 is a perspective view of a flexure pivot bearing.

FIG. 14 is a side view of another transducer constructed in accordancewith the present disclosure.

FIG. 15 is a front elevational view of an inner member.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

This disclosure relates to devices and structures that transmit andmeasure linear forces along and moments about three orthogonal axes. Thedisclosure, including the figures, describes a platform balance andincluded transducers with reference to a several illustrative examples.For example, the disclosure proceeds with respect to frame supportsattached to multi-part transducer assemblies described below. However,it should be noted that the present invention could be implemented inother devices or structures and transducers, as well. The presentinvention is described with respect to the frame supports and transducerassembly for illustrative purposes only. Other examples are contemplatedand are mentioned below or are otherwise imaginable to someone skilledin the art. The scope of the invention is not limited to the fewexamples, i.e., the described embodiments of the invention. Rather, thescope of the invention is defined by reference to the appended claims.Changes can be made to the examples, including alternative designs notdisclosed, and still be within the scope of the claims.

An exemplary embodiment of a platform balance 10 of the presentdisclosure is illustrated in FIGS. 1-3. In the embodiment illustrated,the platform balance 10 can include a first frame support 12 and asecond frame support 14. A plurality of transducer assemblies 16, hereinfour although any number three or more can be used, couple the firstframe support to the second frame support 14. The platform balance 10can be used to measure forces and moments applied to a test specimen ofnominally large weight or mass such as a vehicle, engine, plane, etc.The frame supports 12 and 14 are nominally unstressed reaction frames,wherein each of the transducers comprises a two-axis force transducer.Various levels of flexure isolation can be provided in the platformbalance 10 to provide increased sensitivity, while nominally supportinglarge masses.

Referring to FIGS. 4-6, one of the transducer assemblies is illustratedat 40, wherein each of the transducer assemblies 16 is preferablysimilarly constructed. The transducer assembly 40 includes a sensor body42 and a clevis assembly 44. The clevis assembly 44 includes a firstclevis half 46 and a second clevis half 48. The sensor body 42 isdisposed between the clevis halves 46 and 48 and joined together with asuitable fastener. In the embodiment illustrated, the fastener comprisesa bolt or threaded rod 50 extending through apertures 48A, 42A and 46Aof the clevis half 48, sensor body 42 and clevis half 46, respectively.A nut 51 is provided on an end 53 of rod 50 and a super nut 52 isthreaded upon an end 54 of the threaded rod 50. A plurality of setscrews 56 extends through the apertures in the nut 52 to engage an endof the clevis half 46. Tightening of the set screws 56 allows highclamping pressures to be achieved efficiently and at reduced torquevalues on each of the set screws 56 rather than through the use of a nut52 by itself. It should be noted that although center portions of theclevises 46 and 48 will engage or contact the center portion of thesensor body 42 about the apertures 46A, 42A and 48A, gaps are otherwiseprovided between each of the clevis halves 46 and 48 and the sensor body42 so as to allow the sensor body 42 to move relative to the clevishalves 46 and 48.

The sensor body 42 is preferably integral, being formed of a singleunitary block of material. The sensor body 42 includes a ridged centralhub 60, herein including the aperture 42A, and a ridged perimeter body62 that is concentric with, or disposed about, the central hub 60. Aplurality of flexure structures 64 (herein flexure beams 64 althoughother forms could be used) join the central hub 60 to the perimeter body62. In the embodiment illustrated, the plurality of flexure beams 64comprises four straps 71, 72, 73 and 74. Each of the straps 71-74 extendradially from the central hub 60 to the perimeter body 62 alongcorresponding longitudinal axes 71A, 72A, 73A and 74A. Preferably, axis71A is aligned on axis 73A, while axis 72A is aligned with axis 74A. Inaddition, axes 71A and 73A are perpendicular to axes 72A and 74A.Although illustrated wherein the plurality of flexure beams 64 equalsfour, it should be understood that any number of straps three or morecan be used to join the central hub 60 to the perimeter body 62.Preferably, the flexure beams 64 are spaced at equal angular intervalsabout a central axis indicated at 85.

Flexure members 81, 82, 83 and 84 join an end of each flexure beam71-74, respectively, to the perimeter body 62. The flexure members 81-84are compliant with displacements of each corresponding flexure beam71-74 along the corresponding longitudinal axes 71A-74A. In theembodiment illustrated, the flexure members 81-84 are identical andinclude integrally formed flexure straps 86 and 88. The flexure straps86 and 88 are located on opposite sides of each longitudinal axes71A-74A and joined to corresponding flexure beam 71-74 and to theperimeter body 62.

A sensing device measures displacement or deformation of portions of thesensor body 42. In the body illustrated, a plurality of strain sensors90 are mounted on the flexure beams 64 to sense strain therein. Althoughthe plurality of sensors 90 can be located on the plurality of flexurebeams 64 to provide an indicated of shear stresses, in the embodimentillustrated, the strain sensors are mounted conventionally to provide anoutput signal indicative of bending stresses in the flexure beams 64. Inthe embodiment illustrated, eight strain sensors are provided on thesensor body 42 of each transducer 40 wherein two conventional Wheatstonebridges are formed. A first Wheatstone bridge or sensing circuit isconventionally formed from the strain sensors provided on flexure beam71 and 73, while a second Wheatstone bridge or second sensing circuit isformed from the strain sensors provided on flexure beams 72 and 74. Inanother embodiment, separate Wheatstone bridges can be formed on eachflexure beam 71-74, the outputs of which can be combined as is known inthe art. The plurality of sensors 90 can comprise resistive straingauges. However, other forms of sensing devices such as optically basedsensors or capacitivity based sensors can also be used to measuredeformation or displacement of the flexure beams 64, or other portionsof the sensor body 42 such as each of straps 86 and 88 if desired.

Output signals from the sensing devices are indicative of forcecomponents transmitted between the central hub 60 and the perimeter body62 in two degrees of freedom. For purposes of explanation, a coordinatesystem 97 can be defined wherein an X-axis 97A is aligned with thelongitudinal axes 71A and 73A; a Z-axis 97B is aligned with the verticalaxes 72A and 74A and a Y-axis 97C is aligned with the axis 85.

In the embodiment illustrated, each of the transducer assemblies 16measures two forces. Specifically, a force along the X-axis is measuredas bending stresses created in the flexure beams 72 and 74 since theflexure members 81 and 83 on the ends of the flexure beams 71 and 73 arecompliant in this direction. Similarly, a force along the Z axis ismeasured as bending stresses in the flexure beams 71 and 73 since theflexure members 82 and 84 on the ends of the flexure beams 72 and 74 arecompliant in this direction.

The transducer 40 is also compliant along the axis 85, because offlexures provided on the clevis assembly 44. In the embodimentillustrated, the clevis assembly 44 is formed of substantially identicalclevis halves 46 and 48. In the illustrated embodiment, the sensor 42 isthe “inner member” of the transducer body. Other embodiments arecontemplated. For example, a single clevis half by itself could also beused. Still further, a single clevis half as an inner member connectedto two sensors, which is described later with respect to FIG. 8 couldalso be used.

In the embodiment illustrated, each clevis half 46 and 48 includes acentral hub 102 through which, in the embodiment illustrated, apertures46A and 48A are provided, and a rigid outer body 104. A flexuremechanism couples the rigid central hub 102 with the outer body 104. Inthe embodiment illustrated, a plurality of flexure straps 106 areprovided with a first pair of flexure straps 111 and 112 extending fromthe central hub 102 to a first portion 104A of the outer body 104 and asecond pair of flexure straps 113 and 114 extending from the central hub102 to a second portion 104B of body 104. However, it should be notedthat other forms of flexure members or mechanism can be used between therigid hub 102 and the outer body 104 to allow compliance along axis 85if desired. Such forms can include other integral flexure mechanismssuch as a diaphragm(s), or multi-component assemblies having flexiblecouplings such as slides or pivot connections.

Referring FIGS. 1-3, the sensor body 42 of each of the transducerassemblies 40 is joined to the frame support 12, while each of theclevis halves 46 and 48 of each transducer assembly 40 is joined to aframe support 14. In the embodiment illustrated, mounting plates 120 areused to couple the sensor bodies 42 to the frame support 12, whilemounting plates 122 are used to join the clevis halves 46 and 48 to theframe support 14. In this manner, the frame support 12 provides an innerperimeter frame, while the frame support 14 provides an outer perimeterframe. Use of the mounting plates 120 and 122 allows the frame supports12 and 14 to be nested thereby reducing an overall height of theplatform balance 10.

Each of the frame supports 12 and 14 comprise continuous hollow boxbeams formed in a perimeter so as to provide corresponding stiffassemblies. The frame support 12 holds the sensor bodies 42 in positionwith respect to each other, while the frame support 14 holds the clevisassemblies 44 in position with respect to each other. Stiffening boxframe members 124 can also be provided in the support frame 12 asillustrated.

As appreciated by those skilled in the art, outputs from each of thetwo-axis sensing circuits from each of the transducer assemblies 16 canbe combined so as to sense or provide outputs indicative of forces andmoments upon the platform balance in six degrees of freedom. It shouldbe noted that the flexure mechanisms of the clevis assembly 44 causesthe transducers 16 to operate in a manner similar to how the flexuremembers 81-84 provide compliance in the sensor body 42.

A coordinate system for platform 10 is illustrated at 131 in FIGS. 1 and2. Output signals from transducer assemblies 40A and 40C are used tomeasure forces along the X-axis, because transducer assemblies 40B and40D are compliant in this direction. Likewise, output signals fromtransducer assemblies 40B and 40D are used to measure forces along theY-axis, because transducer assemblies 40A and 40C are compliant in thisdirection. Outputs from all of the transducers 40A-40D are used tomeasure forces along the Z-axis. Overturning moments about the X-axisare measured from the output signals from transducers 40A and 40C; whileoverturning moments about the Y-axis are measured from the outputsignals from transducers 40B and 40D; and while overturning momentsabout the Z-axis are measured from the output signals from transducers40A-40D. Processor 180 receives the output signals from the sensingcircuits of the transducers 40 to calculate forces and/or moments asdesired, typically with respect to the orthogonal coordinate system 131.

As described above, the platform can comprise four two-axis transducerassemblies. This particular design can have advantages over anembodiment having four three-axis (or more) transducer assemblies. Inaddition to the rejection of thermal expansion of the frames 12 and 14relative to each other during lab or tunnel temperature transients, theplatform 10 does not have to reject a relatively large thrust load oneach of the four transducer assemblies (the clevis flexures are all verysoft in thrust (along axis 86) thus shedding load to the two orthogonaltwo-axis transducer assemblies when an x or y side load is applied).This allows the platform 10 to be more optimally tuned for the foursensing flexure straps in each two-axis sensor body 42 than if theassembly was trying to react and measure thrust at the four transducerassembly positions about the platform as in three or more than threeaxis transducer assemblies. The design allows cross axis dimensions andI/c of orthogonal flexure beams to be changed independently to optimizesensitivity. For example, two can be thicker than the other two and canbe thickness variable as well. If the transducer assemblies were threeaxis transducers and this occurred, two of the beams in line with eachother would be stiffer and give different outputs from the orthogonalpair and thus make the sensor behave strangely with off axis or combinedloadings. Lack of need to measure and react to thrust also allows higherstress and strain designs since there is no second bending stress tensorwhich would add bending in an additional axis at beam root connectionsto inner central hubs. Again higher sensitivity, higher resolution andhigher signal to noise ratio with greater span on scalability bothabsolute and measured components relative to each other are provided.

In a further embodiment, over travel stop mechanisms are provided ineach of the transducer assemblies 16 so as to prevent damage to thesensor bodies 42 or flexure mechanisms of the clevis assemblies 44.Referring back to FIGS. 4-6, one or more pins 140 are provided so as tolimit displacement of the sensor body 42 relative to the clevis assembly44. In the embodiment illustrated, apertures 46B, 48B, 42B are providedin the clevis halves 46 and 48 and the sensor body 42, respectively. Thepin 140 is secured, for example, to the sensor body 42 such as by apress fit so that extending portions of the pin 140 extend into theapertures 46B and 48B of the clevis halves 46 and 48 and are nominallyspaced apart from inner walls thereof. If displacement of thedisplaceable portions of the sensor bodies 42 exceeds that desiredrelative to the bodies of the clevis halves 46 and 48, extendingportions of the pin 140 will contact the inner wall of the apertures 46Band/or 48B provided in the clevis half 46 and/or 48 thereby coupling theperimeter body 62 of the sensor body 42 with the outer bodies 104 of theclevis halves 46 and 48 to prevent damage to the flexure straps ormechanism. Note that the perimeter body 62 can be appropriately spacedfrom the clevis half (halves) 46 and/or 48 to provide overtravelprotection. In particular, the perimeter body 62 can engage the clevishalves 46 and/or 48, if displacement along axis 85 exceeds a selecteddistance.

Although the sensor body 42 and clevis halves 46 and 48 can be formedfrom any suitable material, in one embodiment, the sensor body 42 isformed from steel, while the clevis halves are formed from aluminum.Each of the pins 140 can be formed from hardened steel and if necessary,hardened bushings can be provided in the apertures 46B, 48B of theclevis halves 46 and 48 to engage the remote portions of the pin 140. Itshould be noted that the extending portions of the pin 140 can beprovided with a curved or spherical surface 151, as illustrated in FIG.7, relative to a shank portion 153 so as ensure distributed contact ofthe pin 140 with the inner wall of the apertures 46B, 48B formed in theclevis halves 46 and 48.

It should also be noted that depending on the intended application thesensor body 42 and clevis half or halves can be formed a single unitarybody.

FIG. 8 shows an alternative embodiment of the transducer, i.e.,transducer 40′ and corresponding body. Like parts are indicated withlike reference numerals. In this embodiment, one of the clevis halves 46of FIG. 4-6 becomes the inner member. Two sensor members 42 from FIGS.4-6 become the clevis halves. In this example and unlike the previousexamples, the inner member is not instrumented. Rather, the sensormember structures of the previous embodiment are instrumented withsensors, but in this embodiment function as clevis halves. Suitablesensors such as strain gauges 90 are still connected to the members 42.The illustrated example includes twice as many sensors 90 as in theembodiment of FIGS. 4-6. In order to provide usable outputs, the sensorsignals can be combined in each transducer such as by combining orsumming the signals in Wheatstone bridges as is known in the art. Theconfiguration of FIG. 8 is stiffer in the y-direction (as indicated inthe coordinate system) than the embodiment of FIGS. 4-6. The embodimentof FIGS. 4-6, however, is stiffer in a moment about the x-axis than theembodiment of FIG. 8.

FIGS. 9 and 10 illustrate yet another embodiment of a transducer, i.e.,transducer 40″ and corresponding body. Like parts are indicated withlike reference numerals. Transducer 40″ is similar to transducer 40described above in that sensor body 42 is disposed between clevis halves46C and 48C; however in this embodiment clevis halves 46C and 48C aresolid, rigid supports without flexure members therein. As with theembodiments described above, transducer 40″ is a two-axis sensingassembly for sensing forces along the X-axis 97A and Z-axis 97B whensuitable sensors devices are provided for sensor body 42, while beinginsensitive or compliant for forces along the Y-axis 97C. In particular,flexure assemblies 147A and 147B, herein embodied as relatively thinflexible plates, allow the sensor body 42 and clevis halves 46C, 48C tomove freely along the Y-axis 97C, being compliant in that direction, butsubstantially stiff to transfer force loads along the X-axis 97A andZ-axis 97B directions. As illustrated, each flexure assembly 147A, 147Bcan comprise two flexible plates 153, although one or any number ofplates could be used. Flexure assembly 147A is joined to sensor body 42by mounting block 155 and to, for example, frame 12 by mounting block147. Similarly, flexure assembly 147B is joined to clevis halves 46C,48C with clevis tie block 159 and to, for example, frame 14 by mountingblock 161. If desired, the flexure assemblies 147A and 147B can be usedwith all the embodiments described herein. In a further embodiment, theflexure assemblies 147A and 147B can further include cross flexures 169(mounted to blocks 147,155,159 and 161 orthogonal to plates 153), whichallow the flexible plates 153 to be thinner and thus more flexible.

A fastener such as the fastener comprising threaded rod 50 and othercomponents described above joins the clevis halves 46C, 48C to thesensor body 42. It should be noted that although center portions of theclevis halves 46C and 48C will engage or contact the center portion ofthe sensor body 42, gaps are otherwise provided between each of theclevis halves 46C and 48C and the sensor body 42 so as to allow thesensor body 42 to move relative to the clevis halves 46C and 48C. In oneembodiment as illustrated, the clevis halves 46C, 48C and tie block 159are separate components that are fastened together in order that theclevis halves 46C, 48C do not develop a spring force when joined tosensor body 42. In particular, sensor body 42 is first joined to theclevis halves 46C, 48C with the fastener, and then the clevis halves arejoined together with tie block 159.

If desired any of the embodiments herein described can include a torquesensor to measure torque about an axis extending through the couplingjoining the sensor body to the clevis or clevises. The sensed torquevalue can be used for compensation if needed for reducing sensorcrosstalk or compensating for beam stiffness or rotational stiffness ofthe transducers.

Referring by way of example to the embodiment of

FIGS. 9 and 10, the torque sensor can comprise sensors adapted tomeasure strain in flexures of the the sensor body 42. For instance,sensors can comprise strain gauges 170 connected in a Wheatstone bridgeas illustrated in FIG. 12. However, it should be understood any form ofknown electrical, mechanical and/or optically based sensors can be used.

FIG. 11 shows an alternative embodiment of the transducer, i.e.,transducer 40′″ and corresponding body. Like parts are indicated withlike reference numerals. In this embodiment, two sensor members 42 fromFIGS. 9-10 become the clevis halves. In this example and unlike theprevious examples, the inner member 163 is not instrumented and alsorigid. Like the embodiment of FIG. 8, the sensor member structures 42are instrumented with sensors and function as clevis halves, whileflexure assemblies 147A and 147B provide lateral compliance as describedin the previous embodiment, but do not include the cross flexures 169,which can be included if desired. Suitable sensors such as strain gauges90 are still connected to the members 42.

FIG. 14 shows yet another embodiment of the transducer, i.e., transducer40″″ and corresponding body. Like parts are indicated with likereference numerals. In this embodiment, the transducer 40″″ includes asensor assembly 42′ where both the inner member 181 and one or both ofthe outer members 182 (clevis or clevises in the previous embodiments)include sensors (electrical, mechanical or optical) for deflectingelements for sensing strain therein or displacement thereof. Moreparticularly, the load path through the flexure structures 64 of theinner member 181 are connected in series with the corresponding flexurestructures 64 of the outer member(s) 183 for loads along both the X-axis97A and the Z-axis 97B. However, in order to extend the range of thetransducer 40″″, the flexure structures of one of inner member 181 orouter member(s) 183 are designed to be responsive to a first range ofloads, while the other has flexure structures designed to be responsiveto a second range of loads, at least a portion of which is greater thanthat of the first range of loads.

Each of the inner member 181 and outer member(s) 183 has a hub 60 joinedto outer perimeter body 64 with flexure structures 64. Loads aretransferred between the inner member 181 and the outer members(s) 183through the hubs 60, which are connected together. Stated another way,the transducer body 42′ (less the sensing devices) of the transducer40″″ includes at least two sensor bodies 181,183, where each sensor body181,183 has a hub 60 joined to a perimeter body 62 surrounding the hub60 with flexure structures 64. The hubs 60 are joined together and theflexure structures 64 are configured to respond to loads transferredbetween the sensor bodies 181,183 along two orthogonal sensed axes,where the flexure structures 64 of one of the sensor bodies 181,183 hasan operable range greater than the flexure structures 64 of the secondsensor body 181,183. In a further embodiment, as described below, thetransducer body includes an overtravel mechanism to limit deflection ofthe flexure structures 64 of one of the sensor bodies 181,183 andtransfer load to the other sensor body 181,183.

In the embodiment illustrated, by way of example only, the flexurestructures 64 of the inner member 181 are constructed to respond in aknown manner to the first range of loads, while the flexure structuresof the outer member(s) 183 are stiffer and constructed to respond in aknown manner to the second range of loads. In the exemplary embodimentof FIG. 15, the inner member 181 includes strain sensors 185 connectedin two conventional Wheatstone bridges, where sensors 185A are mountedand connected so as to sense loads along axis 97B, while sensors 185Bare mounted and connected so as to sense loads along axis 97A.Similarly, in the embodiment illustrated, one or both of the outermembers 183 can include strain sensors 187 mounted to the flexurestructures 64 thereof like strain sensors 185 are mounted to flexurestructures 64 of inner member 181. In FIG. 14, sensors 187B are similarto sensors 185B, while other sensors (not shown) are similar to sensors185A. Sensors 187 of the outer member(s) 183 provide signal(s)indicative of the second range of loads. Processor 180 can receive allthe signals from the sensing devices for the inner member 181 and theouter member(s) 183 and can include circuitry and/or logic to know whichsignal(s) to use for any load measured by the transducer 40″″.

In view that the inner member 181 has flexure structures more responsive(higher sensitivity) to loads of the first range, overtravel protectionis provided so as to limit displacement of the flexure structures 64 ofthe inner member 181. As appreciated by those skilled in the art,overtravel protection can take many forms, but typically involvescontact of engaging surfaces so as to limit displacement of the flexurestructures. Referring to FIG. 14, one form of overtravel can be providedwith pin 140.

Referring to FIG. 15 and as described above in the previous embodiments,flexure straps 86 and 88 are connected to each of the flexure structures64 so as to provide compliance. In the embodiment illustrated,overtravel protection is provided by stops 191 that contact opposedsurfaces 193 when loads exceeding the first range of loads are beingapplied. In one embodiment, one of the engaging surfaces of the stops191 or its corresponding surface 193 is curved (e.g. part spherical,cylindrical, etc.) so as to allow pivoting motion during contact, ifneeded. It should also be noted the sensitivity of the flexurestructures 64 responsive to loads along the X-axis 97A and Z-axis 97C ofthe inner member 181 and/or outer member(s) 183 may be the same or maybe different. Compliance along the Y-axis 97B can be provided byflexures 153 as described above with respect to the embodiment of FIG.11.

In each of the embodiments described above the sensor body 42 issecurely coupled to the corresponding supporting clevis or clevises atthe center portions thereof. However, in a further embodiment, a pivotconnection can be provided between the sensor body 42 and clevis orclevises. The pivot connection eliminates rotational stiffness of thetransducer.

In one embodiment as illustrated in FIG. 13, a flexure pivot bearing171, can be used in place of fastener 50 to allow the sensor body 42 torotate about an axis extending through the sensor body 42 and thesupporting clevis or clevises, yet the sensor body 42 senses forces intwo orthogonal directions as described above. Flexure pivot bearings arewell known and for instance sold by Riverhawk Company of New Hartford,N.Y., USA. Flexure pivot bearing 171 is suitable for use with a sensorbody joined to portion 173A, while a single support clevis is joined toportion 173B. In embodiments where two support clevises (sensor bodies)are present, a doubled ended flexure pivot bearing is used where twoportions 173B are provided on each side of portion 173A and secured tothe clevises (sensor bodies). As appreciated by those skills in the art,other forms of pivot connections can be used such as but not limited toair bearings, needle bearings and hydrostatic bearings.

The platform balance 10 is particularly well suited for measuring forceand/or moments upon a large specimen such as a vehicle in an environmentsuch as a wind tunnel. In this or similar applications, the platformbalance 10 can include flexures 170 isolating the frame support 12 and14 from the test specimen and a ground support mechanism. In theembodiment illustrated, four flexures 170 are provided between each ofthe transducer assemblies 40, being coupled to the plates 120.Similarly, four flexures 172 are coupled to the mounting plates 122. Theflexure 170, 172 thereby isolate the frame supports 12 and 14. Theflexures 170, 172 are generally aligned with the sensor bodies 42 ofeach corresponding transducer assembly 40.

A counter balance system or assembly is generally provided to supportthe nominal static mass of the test specimen, other components of theoperating environment such as roadways, simulators and components of theplatform balance itself. The counter balance system can take any one ofnumerous forms such as airbags, hydraulic or pneumatic devices, orcables with pulleys and counter weights. An important characteristic ofthe counter balance system is that it is very compliant so as not tointerfere with the sensitivity or measurement of the forces by thetransducers assemblies 40 in order to measure all of the forces andmoments upon the test specimen. In the embodiment illustrated, thecounter balance system is schematically illustrated by actuators 190.

The platform balance 10 is particularly well suited for use in measuringforces upon a vehicle or other large test specimen in a wind tunnel. Insuch an application, rolling roadway belts 182 are supported by anintermediate frame 184 coupled to the flexure members 170. The rollingroadway belts 182 support the vehicle tires. In some embodiments, asingle roadway belt is used for all tires of the vehicle. The platformbalance 10 and rolling roadway belt assemblies 182 are positioned in apit and mounted to a turntable mechanism 186 so as to allow the testspecimen, for example a vehicle, to be selectively turned with respectto the wind of the wind tunnel.

Aspects of the present invention have now been described with referenceto several embodiments. Although the subject matter has been describedin language specific to structural features and/or methodological acts,it is to be understood that the subject matter defined in the appendedclaims is not limited to the specific features or acts described aboveas has been held by the courts. Rather, the specific features and actsdescribed above are disclosed as example forms of implementing theclaims.

1. A platform balance suitable for transmitting forces and moments in aplurality of directions, the platform balance comprising: a framesupport; and at least three spaced-apart transducer bodies coupled tothe frame support, each transducer body, comprising: a supportcomprising a pair of clevis halves; and a sensor body coupled to each ofthe clevis halves, wherein the sensor body is disposed between theclevis halves and adapted to deflect along two orthogonal sensed axesand be rigid along a third axis that is mutually orthogonal to thesensed axes, wherein the sensor body includes a generally rigidperipheral member disposed about a spaced-apart central hub, the centralhub being joined to each of the clevis halves, wherein at least threeflexure structures couple the peripheral member to the central hub, andwherein the flexure structures are spaced-apart from each other atgenerally equal angle intervals about the central hub; and wherein theflexure structures are arranged to be compliant and deflect along thetwo orthogonal axes and be rigid along the third axis.
 2. The platformbalance of claim 13 wherein each clevis halve includes a compliantmember that is compliant in the third axis and rigid in the twoorthogonal axes.
 3. The platform balance of claim 13 wherein the clevishalves are rigid along the two orthogonal sensed axes and the third axisand wherein the clevis halves are joined together remote from thecentral hub.
 4. The platform balance of claim 20 and further comprisinga first flexure assembly coupled to the sensor body and a second flexureassembly coupled to the clevis halves, the first and second flexureassemblies each being compliant along the third axis and rigid alongaxes mutually orthogonal to the third axis.
 5. The platform balance ofclaim 21 wherein the first flexure assembly comprises at least oneflexible plate.
 6. The platform balance of claim 27 wherein the secondflexure assembly comprises at least one flexible plate.
 7. The platformbalance of claim 28 wherein the first flexure assembly comprises a crossflexure.
 8. The platform balance of claim 30 wherein the second flexureassembly comprises a cross flexure.
 9. The platform balance of claim 4wherein the first flexure assembly comprises a plurality of orthogonalflexures wherein one of the flexures is oriented along the third axis.10. The platform balance of claim 9 wherein the second flexure assemblycomprises a plurality of orthogonal flexures wherein one of the flexuresis oriented along the third axis.
 11. The platform balance of claim 1and further comprising a pivot connection joining the sensor body to theclevis halves allowing pivoting motion of the sensor body relative tothe clevis halves about an axis extending through the sensor body andthe clevis halves.
 12. The platform balance of claim 11 wherein thepivot connection is a plurality of orthogonally arranged flexures. 13.The platform balance of claim 11 wherein the pivot connection comprisesa flexure.
 14. The platform balance of claim 1 wherein each flexurestructure of the sensor body comprises a first flexure radially orientedfrom the central hub to the peripheral member and second and thirdflexures joined to an end of the first flexure and extending away fromeach other.
 15. The platform balance of claim 1 and further comprising afirst flexure assembly coupled to the support and a second flexureassembly coupled to the sensor body, the first and second flexureassemblies each being compliant along the third axis and rigid along thesensed axes.
 16. The platform balance of claim 15 wherein the first andsecond flexure assembly each comprises at least one flexible plate. 17.The platform balance of claim 16 wherein the first flexure assemblycomprises a cross flexure.
 18. The platform balance of claim 17 whereinthe second flexure assembly comprises a cross flexure.
 19. The platformbalance of claim 1 wherein the sensor body includes four flexurestructures spaced-apart from each other at generally equal angleintervals about the central hub.
 20. The platform balance of claim 1 incombination with a first frame support, a second frame support and asecond transducer body, wherein the first frame support is coupled tothe sensor body and to a first portion of the second transducer body ata location remote from the sensor body, and wherein the second framesupport is coupled to the support and to a second portion of the secondtransducer body at a location remote from the support.
 21. The platformbalance of claim 20 in combination with a third transducer body and afourth transducer body, wherein a first portion of each of the third andfourth transducer bodies are coupled to the first frame support and asecond portion of each of the third and fourth transducer bodies arecoupled to the second frame support, wherein the transducer body and thesecond transducer body are spaced apart from each other along a firstline, and the third and fourth transducer bodies are spaced apart fromeach other along a second line, the first line and the second line beingorthogonal to each other.
 22. A platform balance suitable fortransmitting forces and moments in a plurality of directions, theplatform balance comprising: a frame support; and at least threespaced-apart transducers coupled to the frame support, each transducerbody, comprising: a first body; a second body having a rigid peripheralmember disposed about a rigid central hub, wherein at least threeflexure structures couple the peripheral member to the central hub, andwherein the flexure structures are spaced-apart from each other atgenerally equal angle intervals about the central hub; a third bodyhaving a rigid peripheral member disposed about a rigid central hub,wherein at least three flexure structures couple the peripheral memberto the central hub, wherein the flexure structures are spaced-apart fromeach other at generally equal angle intervals about the central hub;wherein the central hubs of the second and third bodies are joined tothe first body on opposite sides of the first body and wherein theflexure structures of the second and third bodies are arranged to becompliant and deflect along two orthogonal axes and be rigid along athird axis; a first flexure joined to the first body; a second flexurejoined to the second and third bodies; and wherein the first flexure andsecond flexure are each arranged to be rigid along the two orthogonalaxes and compliant along the third axis.
 23. The platform balance ofclaim 22 and a pivot connection pivotally joining the central hub of thefirst body with the central hubs of the second and third bodies.
 24. Theplatform balance of claim 23 wherein the pivot connection is a pluralityof orthogonally arranged flexures.
 25. A platform balance suitable fortransmitting forces and moments in a plurality of directions, theplatform balance comprising: a frame support; and at least threespaced-apart transducers coupled to the frame support, each transducerbody, comprising: a support comprising a pair of clevis halves; and afirst body coupled to each of the clevis halves, wherein the first bodyis disposed between the clevis halves and adapted to deflect along twoorthogonal axes and be rigid along a third axis that is mutuallyorthogonal to the two orthogonal axes; wherein each of the clevis halvesare rigid along the two orthogonal axes and compliant along the thirdaxis.
 26. The platform balance of claim 25 wherein the first bodyincludes a generally rigid peripheral member disposed about aspaced-apart central hub, wherein at least three flexure structurescouple the peripheral member to the central hub, and wherein the flexurestructures are spaced-apart from each other at generally equal angleintervals about the central hub; and wherein the flexure structures arearranged to be compliant and deflect along the two orthogonal axes andbe rigid along the third axis.
 27. The platform balance of claim 26wherein the first body includes four flexure structures.
 28. Theplatform balance of claim 26 wherein the central hub is coupled to eachof the clevis halves.
 29. The platform balance of claim 26 and furthercomprising a plurality of sensors configured to measure flexure of theflexure structures.
 30. The platform balance of claim 25 wherein each ofthe clevis halves comprise a rigid outer body and a rigid central hub,wherein a plurality of flexures couple the peripheral member to thecentral hub.
 31. The platform balance of claim 30 and a pivot connectionpivotally joining the central hubs of the clevis halves with the centralhub of the first body.
 32. The platform balance of claim 26 wherein eachclevis halve comprises a central hub joined to a perimeter bodysurrounding the central hub with flexure structures, wherein the hub ofthe first body is joined to the hubs of each clevis halve and whereinthe flexure structures of each clevis halve are arranged to respond toloads transferred between the first body along two orthogonal axes, andwherein the flexure structures of the first body has an operable rangedifferent than the flexure structures of the clevis halves.
 33. Theplatform balance of claim 32 and further comprising an overtravelmechanism to limit deflection of the flexure structures of one of thefirst body or the clevis halves and transfer load to the other.
 34. Theplatform balance of claim 30 and further comprising a first flexureassembly coupled to the first body and a second flexure assembly coupledto the clevis halves.
 35. The platform balance of claim 34 wherein thefirst and second flexure assembly each comprises at least one flexibleplate.
 36. The platform balance of claim 35 wherein the first flexureassembly comprises a cross flexure.
 37. The platform balance of claim 36wherein the second flexure assembly comprises a cross flexure.
 38. Aplatform balance suitable for transmitting forces and moments in aplurality of directions, the platform balance comprising: a framesupport; and at least three spaced-apart transducers coupled to theframe support, each transducer body, comprising: a support comprising apair of clevis halves; a sensor body coupled to each of the clevishalves, wherein the sensor body is disposed between the clevis halvesand adapted to deflect along two orthogonal sensed axes and be rigidalong a third axis that is mutually orthogonal to the sensed axes; afirst flexure joined to the sensor body; a second flexure joined to thesupport; and wherein the first flexure and second flexure are eacharranged to be rigid along the two orthogonal sensed axes and compliantalong the third axis.
 39. The platform balance of claim 38 wherein thefirst flexure comprises at least one flexible plate.
 40. The platformbalance of claim 39 wherein the second flexure comprises at least oneflexible plate.
 41. The platform balance of claim 40 wherein the firstflexure and the second flexure each comprise a cross flexure.
 42. Theplatform balance of claim 38 in combination with a first frame support,a second frame support and a second transducer body, wherein the firstframe support is coupled to the first flexure and to a first portion ofthe second transducer body at a location remote from the first flexure,and wherein the second frame support is coupled to the second flexureand to a second portion of the second transducer body at a locationremote from the second flexure.
 43. The platform balance of claim 42 incombination with a third transducer body and a fourth transducer body,wherein a first portion of each of the third and fourth transducerbodies are coupled to the first frame support and a second portion ofeach of the third and fourth transducer bodies are coupled to the secondframe support, wherein the transducer body and the second transducerbody are spaced apart from each other along a first line, and the thirdand fourth transducer bodies are spaced apart from each other along asecond line, the first line and the second line being orthogonal to eachother.
 44. A platform balance suitable for transmitting forces andmoments in a plurality of directions, the platform balance comprising: aframe support; and at least three spaced-apart transducers coupled tothe frame support, each transducer body, comprising: a supportcomprising a pair of clevis halves; and a body coupled to each of theclevis halves, wherein the body is disposed between the clevis halvesand adapted to deflect along two orthogonal axes and be rigid along athird axis that is mutually orthogonal to the two orthogonal axes; apivot connection joining the body to the clevis halves allowing pivotingmotion of the body relative to the clevis halves about an axis extendingthrough the body and the clevis halves, wherein the pivot connection isa plurality of orthogonally arranged flexures.